Women exposed to high levels of pollen in the last third of pregnancy are much more likely to have asthmatic children, suggests research.

It is thought that antibodies produced by the mother in response to pollen may cross into the foetus and make allergies more likely.

A team of Swedish scientists looked at pollen records during the pregnancies of tens of thousands of women.

It is clear that maternal pollen exposure in the last 12 weeks plays a major role

Dr Bertil Forsbery, University of Umea

They reported their results to the Congress of the European Respiratory Society in Stockholm.

They found that women who endured high pollen counts in the last 12 weeks of pregnancy were on average three times more likely to have a baby who developed early asthma.

Dr Bertil Forsberg, who led the research at the University of Umea, said: "It is clear that maternal pollen exposure in the last 12 weeks plays a major role."

However, he said that while this was important, the actual month of birth was not so crucial to the baby's chance of avoiding asthma.

The researchers found that the increase in risk was greatest in babies born in April and May, and lowest in August and September.

Other research, from Serbian scientists at the Belgrade Center for Paediatric Respiratory Medicine, placed more emphasis on month of birth.

It found that babies born in Serbia between April and May, and October and January, were at greater risk of later grass pollen allergy than those born between June and September.

Diet boost

However, two teams of British researchers found that plenty of selenium and iron in the diet of mothers-to-be might actually protect their babies against wheezing.

The scientists, from Kings College London and Bristol University, looked at levels of these minerals in the umbilical cords of more than 2,000 babies.

Higher levels were associated with babies at lower risk of wheezing in early childhood.

Dr Sheelagh Fleming, from the University of Aberdeen, also presented results which suggested that a maternal diet rich in selenium - found in nuts, cereals and fish - and fatty acids found in oily fish was linked to lower risk of wheezing.

In a study of 1,499 children, the risks of such breathing problems in the first year of life were cut by 25% by prenatal maternal diets with plenty of fish oils, and by 12% by those including selenium rich foods.